Kinetics of dynamic recrystallization in low-and medium carbon steels during warm ECA pressing

In this study, electron microscopy was employed to examine the microstructure evolution mechanisms and dynamic recrystallization kinetics in low and medium carbon steels with a lamellar structure of perlite during equal channel angular pressing (ECAP) at 400 degrees C. Mechanisms of the subgrain structure formation and its transformation into a grain-subgrain structure with average element size of 200-500 nm were revealed. It was found that new ultrafine grains with high-angle boundaries are formed in the ferrite phase as a result of dynamic recrystallization beginning after the second ECAP pass. It was shown that the growth rate of the recrystallized fraction increases drastically after 3 ECAP passes. Fragmentation of ferrite lamellas within perlite colonies and strain induced split of cementite plates was detected suppressing the recrystallization in AISI 1045 steel. Enhanced mobility of dislocations in ferrite phase of AISI 1020 steel assisted in severe strain hardening and subsequent dynamic recrystallization. (c) 2020 Elsevier B.V. All rights reserved.